A girl whose family was displaced from their home by fighting in tribal areas receives polio vaccine. Eleven health care workers providing the vaccine have been killed in recent months.

Photo: Muhammed Muheisen, Associated Press

A girl whose family was displaced from their home by fighting in...

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Pakistani relatives and mourners of a polio worker, who was killed in a roadside bomb, pray next to his body, during his funeral procession in Parachinar, capital of Pakistan's tribal region of Kurram along the Afghanistan border, Thursday, Jan. 31, 2013. A roadside bomb killed two Pakistani polio workers on their way to vaccinate children in a northwestern tribal region near the Afghan border on Thursday, an official said. (AP Photo/Dilawar Hussain)

A land mine blast killed two polio vaccination workers in northwest Pakistan on Thursday, the latest deaths involving health care teams trying to eradicate the disease in the South Asian nation.

The blast occurred in Pakistan's Kurram region, one of several remote tribal districts along the border with Afghanistan that have long harbored Islamic militants. Health care workers Muzamel Hussain and Akbar Badshah had been administering polio vaccination drops to children in the village of Malikhel and were on their motorcycle when a mine in the road exploded, Kurram officials said.

In recent months, Pakistani Taliban leaders have denounced vaccination drives by United Nations-backed Pakistani health care workers as a guise for American spying activity, and have unleashed a campaign of targeted attacks against polio vaccination workers across the country. It was not immediately clear whether the men were targeted.

At least 11 vaccination workers have been killed in Pakistan in the past two months. The explosion in Kurram followed two attacks involving vaccination teams this week.

Kurram has a large Shiite Muslim population, and land mines are often used in sectarian violence between Sunni Muslims and Shiites in the area.

Pakistan is one of three countries where polio remains endemic; the other two are Afghanistan and Nigeria. Last year, the number of polio cases in Pakistan dropped to 56, from 173 in 2011.

Caused by a virus that attacks the nervous system, polio is highly communicable and can result in irreversible paralysis within hours of infection. Found more often in countries that lack proper sanitation and hygiene, it mostly affects children under age 5. The virus typically enters the body through the mouth and is spread through fecal contamination of food or beverages.

Pakistani officials have struggled to safeguard polio vaccination teams in the face of persistent attacks from militants. After assailants killed nine vaccination workers in Karachi and northwest Pakistan's Khyber-Pakhtunkhwa province in December, authorities began deploying police to accompany antipolio workers.

Skepticism about polio vaccination drives has also been stoked by radical Islamic clerics who spread rumors that vaccines cause infertility.